1. Field of the Invention
The present invention relates to a process for restoring deactivated catalysts and more particularly a process for efficiently restoring deactivated catalysts for the production of aromatic compounds, containing zeolite and a noble metal or metals of Group VIII of the Periodic Table supported thereon.
2. Description of the Related Art
Various catalysts such as zeolite with a noble metal (e.g., platinum) supported thereon have been known to be effective in the production of aromatic compounds. These catalysts need restoration treatment at suitable intervals because they are deactivated by accumulation of coke on the noble metal after a long term reaction and no longer act as catalysts.
It is well known that coke on a deactivated catalyst (e.g., platinum-supported L-type zeolite) can be removed (decoked) by heating it to temperatures between 430.degree. C. and 540.degree. C. in the presence of diluted oxygen. This decoking at high temperatures causes the agglomeration of the supported noble metal particles, that is, a decrease in the surface area of the noble metal particles, which will lead to a decrease of catalytic activity. Therefore, it is necessary after the high temperature decoking that the catalyst is brought in contact with air and chlorine or a chlorine compound such as carbon tetrachloride at an elevated temperature (oxychlorination treatment) to redisperse the noble metal particles (see Japanese patent application Laid-Open Nos. 168540/1985 and 55045/1983).
By the above oxychlorination treatment, however, it is quite difficult to restore catalysts poisoned with sulfur or those extremely deactivated.